Angle-resolved photoemission study of the graphite intercalation compound KC8: A key to graphene

Electrons in isolated graphene layers are a two-dimensional gas of massless Dirac Fermions. In realistic devices, however, the electronic properties are modified by elastic deformations, interlayer coupling and substrate interaction. Here, we unravel the electronic structure of noninteracting, doped graphene layers by revisiting the stage one graphite intercalation compound KC8. To this end we apply angle-resolved photoemission spectroscopy and ab initio calculations. The full experimental dispersion is in excellent agreement with calculations of doped graphene once electron correlations are included at the GW level (Greens function G of the Coulomb interaction W). This highlights that KC8 has negligible interlayer coupling allowing us to access the full experimental Dirac cone.